Permeation of molecules through a polymer depends on several factors including the polymers' crystallinity, chain stiffness, molecular orientation, free volume, cohesive energy density, and the ability of the polymer to absorb the permeant molecule. In particular cases, the permeation properties of a given polymer depend on the available free volume within the polymer, and the ease with which polymer chains can re-arrange or relax to increase the free volume. Therefore, as the free volume of the polymer is increased, a molecule may more easily diffuse or permeate through the polymer.
Ethylene vinyl alcohol (EVOH) is a polymer that is produced by complete hydrolysis of random co-polymers of ethylene vinyl acetate and is widely used in food packaging and other barrier films due to its high-barrier and low permeation properties toward gases. The permeation properties of EVOH are largely dependent on the copolymerization ratio of ethylene and vinyl alcohol and high inter- and intra-molecular cohesive energy facilitated by the strong inter- and intra-polymer chain hydrogen bonding. The existing inter- and intra-chain bonding restricts the segmental motion of EVOH polymer chains and reduces the ability of these chains to re-arrange or relax limiting the free volume within the polymer and inhibiting diffusion of permeant molecules.
Barrier films incorporating EVOH polymers are currently used to provide protection against gaseous species such as oxygen, carbon dioxide, aromatic compounds and water vapor.
Accordingly, it is an object of this disclosure to provide a polymer nanocomposite with improved barrier and low permeation properties towards gaseous species such as oxygen, carbon dioxide and water vapor and increased barrier protection against chemical warfare agents such as mustard gas (HD), G-series nerve agents like Sarin (GB), Soman (GD) and V-series nerve agents (VX) for greater than about 72 hours. It is also an object of the disclosure to provide a multilayer barrier film that includes a polymer nanocomposite having improved barrier and low permeation properties that is flame retardant.